$749.00 MSRP

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The field strength meter is a cost effective and simple solution for measuring, setting up and commissioning a hearing loop system to the requirements of IEC60118:2006 standard. The meter is an ergonomically designed hand held instrument for measuring loop system performance. There are three calibrated operational modes for the assessment of background noise, field strength and frequency response as required to ensure correct function of the loop system. The meter also doubles as a loop receiver with a headphone output to listen to the signal in the loop.


One (1) FSM Field Strength Meter
One (1) Audio CD with Test Signals
Two (2) AA Alkaline Batteries
One (1) Soft Carrying Pouch
One (1) Instruction Guide


  • Cost effective simple solution for measuring, setting up and commissioning a hearing loop system to the requirements of IEC60118-4, updated in 2006
  • Three modes of operations for three test types. A-weighted background noise, broad band mode (50 Hz – 8 kHz) and frequency response (100 Hz, 1 kHz, 5 kHz)
Configurations & Architectural Specs


FSM Field Strength Meter

Architectural Specs

The field strength meter shall measure the background noise by determining the level of background magnetic field present in the intended location for the loop system. It shall measure the field strength delivered by the system. The meter shall measure the performance of the frequency spectrum required by IEC60118:2006 standard. It shall have an audio output to allow to the signal to be heard through a headphone or earspeaker. The meter shall include a LED graph with a wide view angle that is color coded. It shall accept two (2) AA alkaline batteries and display an illuminated LED when the battery is at acceptable level. The FSM Field Strength Meter is specified.

Product Specifications


Frequency Response50 Hz to 8 kHz ±0.25 dB, 30 Hz to 10 kHz -3 dB
Gain StabilityBetter then 0.5 dB over all conditions


LEDsColor Coded - Green for -3 to +3 dB, Red for -4 to -22 dB


Headphone Connector3.5 mm Stereo Connector, 16 Ohms (32 Ohms per side)


Coil OrientationVertical when held upright
Reference Level400 mA/m (In field strength mode)


Battery TypeTwo (2) x AA Alkaline
Battery LifeUp to 100 hrs. use, dependant on use pattern
Battery MonitorBattery OK when LED illuminated


Width3.3 in. (84 mm)
Height5.5 in. (140 mm)
Depth1.0 in. (27 mm)
Shipping Weight1.2 lbs. (0.54 kg)
Weight1.2 lbs. (0.54 kg)


Relative HumidityIP20 Protection, 20 to 90% Relative Humidity, 14 F (-10 C) to 113 F (45 C)
Used With
QWhat is Listen Technologies product warranty?
AClick for Listen's product warranty.
QShould I purchase a field strength meter?
AAbsolutely, it’s the only way you’ll be able to determine if a loop system is operating properly. Any venue that owns and operates a loop system should also have some equipment to monitor the operation of the loop on a regular basis. This should either be a field strength meter (R1), (FSM) or a receiver with field strength indication (IR-IL-1).
QWhat is an array system and how do I design one?
AAn array uses two loop drivers and an SP5 phase shifter to create two overlaid magnetic fields, capable of accurately controlling the field within and around the loop system. They can be used to prevent ‘spill’ of magnetic field allowing loops to be used in adjacent rooms, and to give good even coverage in areas with metal building structures or complex installations. Arrays need a special layout design that can be provided by Listen. Arrays will always give a better field coverage and higher certainty of excellent performance than a perimeter loop, however the installation is more demanding and requires loop cables to cross the floor or ceiling of the area of use.
QWhat audio input should I use on an induction/hearing loop?
AEither an existing audio system can be used, or a dedicated microphone or other audio source may need to be provided. The objective is to ensure the loop system receives the required audio source (e.g. a voice) and not any background noise. The most essential job of any assistive listening system is to increase the level of the signal (the voice) relative to the background.
QWhich type of cable should I use for an induction/hearing loop?
AFor cable intended to go under a carpet, you should use 1.8mm2 flat copper tape. Otherwise, you should choose the cable based on the maximum total cable length in the specifications chart.
QWhat is spill or overspill?
AOverspill occurs when the magnetic field created by hearing loop can be heard outside of the looped area (such as a room). The field is “spilling” outside of the looped area and can affect other nearby loop systems.
QHow do you minimize overspill?
AThis is done by using an array, consisting of two loop drivers and a SP5 phase shifter that controls the field within the looped area and reduces it rapidly outside the loop perimeter. The overspill can be reduced to as little as 5 ft (1.5m) with a good design.
QWhat is metal loss correction?
AMany buildings have embedded metal in the structure such as reinforcements in concrete, metal computer floors or suspended ceiling grids. This metal causes a distortion of the frequency response if the metal is in the same plane as the loop cable. The metal loss correction equalizes the audio to make up for or “correct” this loss. Note that metal loss will also reduce the signal level in general, and may require additional power, or indeed an array system to achieve the right level of performance.
QWhy do loop drivers have extensive audio processing?
ABecause the people who benefit from hearing loops (individuals with t-coil hearing aids), have limited dynamic range due to hearing loss. Thus, these users require significantly reduced dynamic range so they can hear the softest of sounds and so that very loud sounds are brought to nominal level.
QHow do I choose which loop driver is best for my installation?
AGenerally, this depends on the size of the room, the construction of the building, and the type of loop system you need. Refer to the Designing a Hearing Loop System Guide and Listen support to help you specify and design your system.
QWhen should I use a perimeter loop system and when do I need an array?
AA perimeter loop is the simplest form of loop system requiring a single loop of cable around the area to be used. However perimeter loops cannot be used if (1) other loop systems or areas where t-coil receivers are used are nearer than 3 times the room width (shortest side); (2) the room width is over 15ft and there is significant metal in the plane of the loop, such as reinforcement in a concrete floor. In these cases an array system is usually required. You may be able to conduct a site survey to confirm whether an array is necessary – contact Listen for details.
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